This project will focus on chondroitin sulfate (CS) glycosaminoglycans, a class of polysaccharides that play important roles in development, viral invasion, cancer, and spinal cord injury. CS polysaccharides display diverse sulfation patterns that are spatiotemporally regulated in vivo. However, efforts to identify functions for specific sulfation motifs have been hampered by the structural complexity of CS and a lack of tools. For instance, well-defined CS molecules cannot be purified from natural sources, and as a consequence, the field has been limited to working with heterogeneously sulfated mixtures of compounds. Genetic deletion of one of the sulfotransferase genes responsible for CS biosynthesis can propagate global changes throughout the carbohydrate chain, making it difficult to pinpoint the role of specific sulfation motifs. In this grant, we will combine the tools of organic chemistry and biology to overcome these challenges. We will exploit synthetic chemistry to assemble defined CS structures (both natural and non-natural) to obtain fundamentally new information about the structure- function relationships of CS. When combined with the power of biochemistry, genetics, cell biology, and neurobiology, these molecules will provide new insights into the physiological roles of carbohydrates in the nervous system and uncover novel mechanisms of neuronal growth and repair. As our project takes a distinctly chemical approach, this work may reveal novel proteins and pathways for therapeutic intervention and aid in the development of new pharmaceuticals to stimulate regeneration after injury, aging or disease.